Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * auth-scram.c
4 : * Server-side implementation of the SASL SCRAM-SHA-256 mechanism.
5 : *
6 : * See the following RFCs for more details:
7 : * - RFC 5802: https://tools.ietf.org/html/rfc5802
8 : * - RFC 5803: https://tools.ietf.org/html/rfc5803
9 : * - RFC 7677: https://tools.ietf.org/html/rfc7677
10 : *
11 : * Here are some differences:
12 : *
13 : * - Username from the authentication exchange is not used. The client
14 : * should send an empty string as the username.
15 : *
16 : * - If the password isn't valid UTF-8, or contains characters prohibited
17 : * by the SASLprep profile, we skip the SASLprep pre-processing and use
18 : * the raw bytes in calculating the hash.
19 : *
20 : * - If channel binding is used, the channel binding type is always
21 : * "tls-server-end-point". The spec says the default is "tls-unique"
22 : * (RFC 5802, section 6.1. Default Channel Binding), but there are some
23 : * problems with that. Firstly, not all SSL libraries provide an API to
24 : * get the TLS Finished message, required to use "tls-unique". Secondly,
25 : * "tls-unique" is not specified for TLS v1.3, and as of this writing,
26 : * it's not clear if there will be a replacement. We could support both
27 : * "tls-server-end-point" and "tls-unique", but for our use case,
28 : * "tls-unique" doesn't really have any advantages. The main advantage
29 : * of "tls-unique" would be that it works even if the server doesn't
30 : * have a certificate, but PostgreSQL requires a server certificate
31 : * whenever SSL is used, anyway.
32 : *
33 : *
34 : * The password stored in pg_authid consists of the iteration count, salt,
35 : * StoredKey and ServerKey.
36 : *
37 : * SASLprep usage
38 : * --------------
39 : *
40 : * One notable difference to the SCRAM specification is that while the
41 : * specification dictates that the password is in UTF-8, and prohibits
42 : * certain characters, we are more lenient. If the password isn't a valid
43 : * UTF-8 string, or contains prohibited characters, the raw bytes are used
44 : * to calculate the hash instead, without SASLprep processing. This is
45 : * because PostgreSQL supports other encodings too, and the encoding being
46 : * used during authentication is undefined (client_encoding isn't set until
47 : * after authentication). In effect, we try to interpret the password as
48 : * UTF-8 and apply SASLprep processing, but if it looks invalid, we assume
49 : * that it's in some other encoding.
50 : *
51 : * In the worst case, we misinterpret a password that's in a different
52 : * encoding as being Unicode, because it happens to consists entirely of
53 : * valid UTF-8 bytes, and we apply Unicode normalization to it. As long
54 : * as we do that consistently, that will not lead to failed logins.
55 : * Fortunately, the UTF-8 byte sequences that are ignored by SASLprep
56 : * don't correspond to any commonly used characters in any of the other
57 : * supported encodings, so it should not lead to any significant loss in
58 : * entropy, even if the normalization is incorrectly applied to a
59 : * non-UTF-8 password.
60 : *
61 : * Error handling
62 : * --------------
63 : *
64 : * Don't reveal user information to an unauthenticated client. We don't
65 : * want an attacker to be able to probe whether a particular username is
66 : * valid. In SCRAM, the server has to read the salt and iteration count
67 : * from the user's stored secret, and send it to the client. To avoid
68 : * revealing whether a user exists, when the client tries to authenticate
69 : * with a username that doesn't exist, or doesn't have a valid SCRAM
70 : * secret in pg_authid, we create a fake salt and iteration count
71 : * on-the-fly, and proceed with the authentication with that. In the end,
72 : * we'll reject the attempt, as if an incorrect password was given. When
73 : * we are performing a "mock" authentication, the 'doomed' flag in
74 : * scram_state is set.
75 : *
76 : * In the error messages, avoid printing strings from the client, unless
77 : * you check that they are pure ASCII. We don't want an unauthenticated
78 : * attacker to be able to spam the logs with characters that are not valid
79 : * to the encoding being used, whatever that is. We cannot avoid that in
80 : * general, after logging in, but let's do what we can here.
81 : *
82 : *
83 : * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
84 : * Portions Copyright (c) 1994, Regents of the University of California
85 : *
86 : * src/backend/libpq/auth-scram.c
87 : *
88 : *-------------------------------------------------------------------------
89 : */
90 : #include "postgres.h"
91 :
92 : #include <unistd.h>
93 :
94 : #include "access/xlog.h"
95 : #include "catalog/pg_authid.h"
96 : #include "catalog/pg_control.h"
97 : #include "common/base64.h"
98 : #include "common/saslprep.h"
99 : #include "common/scram-common.h"
100 : #include "common/sha2.h"
101 : #include "libpq/auth.h"
102 : #include "libpq/crypt.h"
103 : #include "libpq/scram.h"
104 : #include "miscadmin.h"
105 : #include "utils/builtins.h"
106 : #include "utils/timestamp.h"
107 :
108 : /*
109 : * Status data for a SCRAM authentication exchange. This should be kept
110 : * internal to this file.
111 : */
112 : typedef enum
113 : {
114 : SCRAM_AUTH_INIT,
115 : SCRAM_AUTH_SALT_SENT,
116 : SCRAM_AUTH_FINISHED
117 : } scram_state_enum;
118 :
119 : typedef struct
120 : {
121 : scram_state_enum state;
122 :
123 : const char *username; /* username from startup packet */
124 :
125 : Port *port;
126 : bool channel_binding_in_use;
127 :
128 : int iterations;
129 : char *salt; /* base64-encoded */
130 : uint8 StoredKey[SCRAM_KEY_LEN];
131 : uint8 ServerKey[SCRAM_KEY_LEN];
132 :
133 : /* Fields of the first message from client */
134 : char cbind_flag;
135 : char *client_first_message_bare;
136 : char *client_username;
137 : char *client_nonce;
138 :
139 : /* Fields from the last message from client */
140 : char *client_final_message_without_proof;
141 : char *client_final_nonce;
142 : char ClientProof[SCRAM_KEY_LEN];
143 :
144 : /* Fields generated in the server */
145 : char *server_first_message;
146 : char *server_nonce;
147 :
148 : /*
149 : * If something goes wrong during the authentication, or we are performing
150 : * a "mock" authentication (see comments at top of file), the 'doomed'
151 : * flag is set. A reason for the failure, for the server log, is put in
152 : * 'logdetail'.
153 : */
154 : bool doomed;
155 : char *logdetail;
156 : } scram_state;
157 :
158 : static void read_client_first_message(scram_state *state, const char *input);
159 : static void read_client_final_message(scram_state *state, const char *input);
160 : static char *build_server_first_message(scram_state *state);
161 : static char *build_server_final_message(scram_state *state);
162 : static bool verify_client_proof(scram_state *state);
163 : static bool verify_final_nonce(scram_state *state);
164 : static void mock_scram_secret(const char *username, int *iterations,
165 : char **salt, uint8 *stored_key, uint8 *server_key);
166 : static bool is_scram_printable(char *p);
167 : static char *sanitize_char(char c);
168 : static char *sanitize_str(const char *s);
169 : static char *scram_mock_salt(const char *username);
170 :
171 : /*
172 : * pg_be_scram_get_mechanisms
173 : *
174 : * Get a list of SASL mechanisms that this module supports.
175 : *
176 : * For the convenience of building the FE/BE packet that lists the
177 : * mechanisms, the names are appended to the given StringInfo buffer,
178 : * separated by '\0' bytes.
179 : */
180 : void
181 38 : pg_be_scram_get_mechanisms(Port *port, StringInfo buf)
182 : {
183 : /*
184 : * Advertise the mechanisms in decreasing order of importance. So the
185 : * channel-binding variants go first, if they are supported. Channel
186 : * binding is only supported with SSL, and only if the SSL implementation
187 : * has a function to get the certificate's hash.
188 : */
189 : #ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
190 38 : if (port->ssl_in_use)
191 : {
192 6 : appendStringInfoString(buf, SCRAM_SHA_256_PLUS_NAME);
193 6 : appendStringInfoChar(buf, '\0');
194 : }
195 : #endif
196 38 : appendStringInfoString(buf, SCRAM_SHA_256_NAME);
197 38 : appendStringInfoChar(buf, '\0');
198 38 : }
199 :
200 : /*
201 : * pg_be_scram_init
202 : *
203 : * Initialize a new SCRAM authentication exchange status tracker. This
204 : * needs to be called before doing any exchange. It will be filled later
205 : * after the beginning of the exchange with authentication information.
206 : *
207 : * 'selected_mech' identifies the SASL mechanism that the client selected.
208 : * It should be one of the mechanisms that we support, as returned by
209 : * pg_be_scram_get_mechanisms().
210 : *
211 : * 'shadow_pass' is the role's stored secret, from pg_authid.rolpassword.
212 : * The username was provided by the client in the startup message, and is
213 : * available in port->user_name. If 'shadow_pass' is NULL, we still perform
214 : * an authentication exchange, but it will fail, as if an incorrect password
215 : * was given.
216 : */
217 : void *
218 36 : pg_be_scram_init(Port *port,
219 : const char *selected_mech,
220 : const char *shadow_pass)
221 : {
222 : scram_state *state;
223 : bool got_secret;
224 :
225 36 : state = (scram_state *) palloc0(sizeof(scram_state));
226 36 : state->port = port;
227 36 : state->state = SCRAM_AUTH_INIT;
228 :
229 : /*
230 : * Parse the selected mechanism.
231 : *
232 : * Note that if we don't support channel binding, either because the SSL
233 : * implementation doesn't support it or we're not using SSL at all, we
234 : * would not have advertised the PLUS variant in the first place. If the
235 : * client nevertheless tries to select it, it's a protocol violation like
236 : * selecting any other SASL mechanism we don't support.
237 : */
238 : #ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
239 36 : if (strcmp(selected_mech, SCRAM_SHA_256_PLUS_NAME) == 0 && port->ssl_in_use)
240 4 : state->channel_binding_in_use = true;
241 : else
242 : #endif
243 32 : if (strcmp(selected_mech, SCRAM_SHA_256_NAME) == 0)
244 32 : state->channel_binding_in_use = false;
245 : else
246 0 : ereport(ERROR,
247 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
248 : errmsg("client selected an invalid SASL authentication mechanism")));
249 :
250 : /*
251 : * Parse the stored secret.
252 : */
253 36 : if (shadow_pass)
254 : {
255 36 : int password_type = get_password_type(shadow_pass);
256 :
257 36 : if (password_type == PASSWORD_TYPE_SCRAM_SHA_256)
258 : {
259 34 : if (parse_scram_secret(shadow_pass, &state->iterations, &state->salt,
260 34 : state->StoredKey, state->ServerKey))
261 34 : got_secret = true;
262 : else
263 : {
264 : /*
265 : * The password looked like a SCRAM secret, but could not be
266 : * parsed.
267 : */
268 0 : ereport(LOG,
269 : (errmsg("invalid SCRAM secret for user \"%s\"",
270 : state->port->user_name)));
271 0 : got_secret = false;
272 : }
273 : }
274 : else
275 : {
276 : /*
277 : * The user doesn't have SCRAM secret. (You cannot do SCRAM
278 : * authentication with an MD5 hash.)
279 : */
280 4 : state->logdetail = psprintf(_("User \"%s\" does not have a valid SCRAM secret."),
281 2 : state->port->user_name);
282 2 : got_secret = false;
283 : }
284 : }
285 : else
286 : {
287 : /*
288 : * The caller requested us to perform a dummy authentication. This is
289 : * considered normal, since the caller requested it, so don't set log
290 : * detail.
291 : */
292 0 : got_secret = false;
293 : }
294 :
295 : /*
296 : * If the user did not have a valid SCRAM secret, we still go through the
297 : * motions with a mock one, and fail as if the client supplied an
298 : * incorrect password. This is to avoid revealing information to an
299 : * attacker.
300 : */
301 36 : if (!got_secret)
302 : {
303 2 : mock_scram_secret(state->port->user_name, &state->iterations,
304 2 : &state->salt, state->StoredKey, state->ServerKey);
305 2 : state->doomed = true;
306 : }
307 :
308 36 : return state;
309 : }
310 :
311 : /*
312 : * Continue a SCRAM authentication exchange.
313 : *
314 : * 'input' is the SCRAM payload sent by the client. On the first call,
315 : * 'input' contains the "Initial Client Response" that the client sent as
316 : * part of the SASLInitialResponse message, or NULL if no Initial Client
317 : * Response was given. (The SASL specification distinguishes between an
318 : * empty response and non-existing one.) On subsequent calls, 'input'
319 : * cannot be NULL. For convenience in this function, the caller must
320 : * ensure that there is a null terminator at input[inputlen].
321 : *
322 : * The next message to send to client is saved in 'output', for a length
323 : * of 'outputlen'. In the case of an error, optionally store a palloc'd
324 : * string at *logdetail that will be sent to the postmaster log (but not
325 : * the client).
326 : */
327 : int
328 72 : pg_be_scram_exchange(void *opaq, const char *input, int inputlen,
329 : char **output, int *outputlen, char **logdetail)
330 : {
331 72 : scram_state *state = (scram_state *) opaq;
332 : int result;
333 :
334 72 : *output = NULL;
335 :
336 : /*
337 : * If the client didn't include an "Initial Client Response" in the
338 : * SASLInitialResponse message, send an empty challenge, to which the
339 : * client will respond with the same data that usually comes in the
340 : * Initial Client Response.
341 : */
342 72 : if (input == NULL)
343 : {
344 : Assert(state->state == SCRAM_AUTH_INIT);
345 :
346 0 : *output = pstrdup("");
347 0 : *outputlen = 0;
348 0 : return SASL_EXCHANGE_CONTINUE;
349 : }
350 :
351 : /*
352 : * Check that the input length agrees with the string length of the input.
353 : * We can ignore inputlen after this.
354 : */
355 72 : if (inputlen == 0)
356 0 : ereport(ERROR,
357 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
358 : errmsg("malformed SCRAM message"),
359 : errdetail("The message is empty.")));
360 72 : if (inputlen != strlen(input))
361 0 : ereport(ERROR,
362 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
363 : errmsg("malformed SCRAM message"),
364 : errdetail("Message length does not match input length.")));
365 :
366 72 : switch (state->state)
367 : {
368 36 : case SCRAM_AUTH_INIT:
369 :
370 : /*
371 : * Initialization phase. Receive the first message from client
372 : * and be sure that it parsed correctly. Then send the challenge
373 : * to the client.
374 : */
375 36 : read_client_first_message(state, input);
376 :
377 : /* prepare message to send challenge */
378 36 : *output = build_server_first_message(state);
379 :
380 36 : state->state = SCRAM_AUTH_SALT_SENT;
381 36 : result = SASL_EXCHANGE_CONTINUE;
382 36 : break;
383 :
384 36 : case SCRAM_AUTH_SALT_SENT:
385 :
386 : /*
387 : * Final phase for the server. Receive the response to the
388 : * challenge previously sent, verify, and let the client know that
389 : * everything went well (or not).
390 : */
391 36 : read_client_final_message(state, input);
392 :
393 36 : if (!verify_final_nonce(state))
394 0 : ereport(ERROR,
395 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
396 : errmsg("invalid SCRAM response"),
397 : errdetail("Nonce does not match.")));
398 :
399 : /*
400 : * Now check the final nonce and the client proof.
401 : *
402 : * If we performed a "mock" authentication that we knew would fail
403 : * from the get go, this is where we fail.
404 : *
405 : * The SCRAM specification includes an error code,
406 : * "invalid-proof", for authentication failure, but it also allows
407 : * erroring out in an application-specific way. We choose to do
408 : * the latter, so that the error message for invalid password is
409 : * the same for all authentication methods. The caller will call
410 : * ereport(), when we return SASL_EXCHANGE_FAILURE with no output.
411 : *
412 : * NB: the order of these checks is intentional. We calculate the
413 : * client proof even in a mock authentication, even though it's
414 : * bound to fail, to thwart timing attacks to determine if a role
415 : * with the given name exists or not.
416 : */
417 36 : if (!verify_client_proof(state) || state->doomed)
418 : {
419 10 : result = SASL_EXCHANGE_FAILURE;
420 10 : break;
421 : }
422 :
423 : /* Build final message for client */
424 26 : *output = build_server_final_message(state);
425 :
426 : /* Success! */
427 26 : result = SASL_EXCHANGE_SUCCESS;
428 26 : state->state = SCRAM_AUTH_FINISHED;
429 26 : break;
430 :
431 0 : default:
432 0 : elog(ERROR, "invalid SCRAM exchange state");
433 : result = SASL_EXCHANGE_FAILURE;
434 : }
435 :
436 72 : if (result == SASL_EXCHANGE_FAILURE && state->logdetail && logdetail)
437 2 : *logdetail = state->logdetail;
438 :
439 72 : if (*output)
440 62 : *outputlen = strlen(*output);
441 :
442 72 : return result;
443 : }
444 :
445 : /*
446 : * Construct a SCRAM secret, for storing in pg_authid.rolpassword.
447 : *
448 : * The result is palloc'd, so caller is responsible for freeing it.
449 : */
450 : char *
451 44 : pg_be_scram_build_secret(const char *password)
452 : {
453 : char *prep_password;
454 : pg_saslprep_rc rc;
455 : char saltbuf[SCRAM_DEFAULT_SALT_LEN];
456 : char *result;
457 :
458 : /*
459 : * Normalize the password with SASLprep. If that doesn't work, because
460 : * the password isn't valid UTF-8 or contains prohibited characters, just
461 : * proceed with the original password. (See comments at top of file.)
462 : */
463 44 : rc = pg_saslprep(password, &prep_password);
464 44 : if (rc == SASLPREP_SUCCESS)
465 42 : password = (const char *) prep_password;
466 :
467 : /* Generate random salt */
468 44 : if (!pg_strong_random(saltbuf, SCRAM_DEFAULT_SALT_LEN))
469 0 : ereport(ERROR,
470 : (errcode(ERRCODE_INTERNAL_ERROR),
471 : errmsg("could not generate random salt")));
472 :
473 44 : result = scram_build_secret(saltbuf, SCRAM_DEFAULT_SALT_LEN,
474 : SCRAM_DEFAULT_ITERATIONS, password);
475 :
476 44 : if (prep_password)
477 42 : pfree(prep_password);
478 :
479 44 : return result;
480 : }
481 :
482 : /*
483 : * Verify a plaintext password against a SCRAM secret. This is used when
484 : * performing plaintext password authentication for a user that has a SCRAM
485 : * secret stored in pg_authid.
486 : */
487 : bool
488 14 : scram_verify_plain_password(const char *username, const char *password,
489 : const char *secret)
490 : {
491 : char *encoded_salt;
492 : char *salt;
493 : int saltlen;
494 : int iterations;
495 : uint8 salted_password[SCRAM_KEY_LEN];
496 : uint8 stored_key[SCRAM_KEY_LEN];
497 : uint8 server_key[SCRAM_KEY_LEN];
498 : uint8 computed_key[SCRAM_KEY_LEN];
499 : char *prep_password;
500 : pg_saslprep_rc rc;
501 :
502 14 : if (!parse_scram_secret(secret, &iterations, &encoded_salt,
503 : stored_key, server_key))
504 : {
505 : /*
506 : * The password looked like a SCRAM secret, but could not be parsed.
507 : */
508 0 : ereport(LOG,
509 : (errmsg("invalid SCRAM secret for user \"%s\"", username)));
510 0 : return false;
511 : }
512 :
513 14 : saltlen = pg_b64_dec_len(strlen(encoded_salt));
514 14 : salt = palloc(saltlen);
515 14 : saltlen = pg_b64_decode(encoded_salt, strlen(encoded_salt), salt,
516 : saltlen);
517 14 : if (saltlen < 0)
518 : {
519 0 : ereport(LOG,
520 : (errmsg("invalid SCRAM secret for user \"%s\"", username)));
521 0 : return false;
522 : }
523 :
524 : /* Normalize the password */
525 14 : rc = pg_saslprep(password, &prep_password);
526 14 : if (rc == SASLPREP_SUCCESS)
527 14 : password = prep_password;
528 :
529 : /* Compute Server Key based on the user-supplied plaintext password */
530 14 : scram_SaltedPassword(password, salt, saltlen, iterations, salted_password);
531 14 : scram_ServerKey(salted_password, computed_key);
532 :
533 14 : if (prep_password)
534 14 : pfree(prep_password);
535 :
536 : /*
537 : * Compare the secret's Server Key with the one computed from the
538 : * user-supplied password.
539 : */
540 14 : return memcmp(computed_key, server_key, SCRAM_KEY_LEN) == 0;
541 : }
542 :
543 :
544 : /*
545 : * Parse and validate format of given SCRAM secret.
546 : *
547 : * On success, the iteration count, salt, stored key, and server key are
548 : * extracted from the secret, and returned to the caller. For 'stored_key'
549 : * and 'server_key', the caller must pass pre-allocated buffers of size
550 : * SCRAM_KEY_LEN. Salt is returned as a base64-encoded, null-terminated
551 : * string. The buffer for the salt is palloc'd by this function.
552 : *
553 : * Returns true if the SCRAM secret has been parsed, and false otherwise.
554 : */
555 : bool
556 292 : parse_scram_secret(const char *secret, int *iterations, char **salt,
557 : uint8 *stored_key, uint8 *server_key)
558 : {
559 : char *v;
560 : char *p;
561 : char *scheme_str;
562 : char *salt_str;
563 : char *iterations_str;
564 : char *storedkey_str;
565 : char *serverkey_str;
566 : int decoded_len;
567 : char *decoded_salt_buf;
568 : char *decoded_stored_buf;
569 : char *decoded_server_buf;
570 :
571 : /*
572 : * The secret is of form:
573 : *
574 : * SCRAM-SHA-256$<iterations>:<salt>$<storedkey>:<serverkey>
575 : */
576 292 : v = pstrdup(secret);
577 292 : if ((scheme_str = strtok(v, "$")) == NULL)
578 0 : goto invalid_secret;
579 292 : if ((iterations_str = strtok(NULL, ":")) == NULL)
580 128 : goto invalid_secret;
581 164 : if ((salt_str = strtok(NULL, "$")) == NULL)
582 8 : goto invalid_secret;
583 156 : if ((storedkey_str = strtok(NULL, ":")) == NULL)
584 0 : goto invalid_secret;
585 156 : if ((serverkey_str = strtok(NULL, "")) == NULL)
586 0 : goto invalid_secret;
587 :
588 : /* Parse the fields */
589 156 : if (strcmp(scheme_str, "SCRAM-SHA-256") != 0)
590 0 : goto invalid_secret;
591 :
592 156 : errno = 0;
593 156 : *iterations = strtol(iterations_str, &p, 10);
594 156 : if (*p || errno != 0)
595 0 : goto invalid_secret;
596 :
597 : /*
598 : * Verify that the salt is in Base64-encoded format, by decoding it,
599 : * although we return the encoded version to the caller.
600 : */
601 156 : decoded_len = pg_b64_dec_len(strlen(salt_str));
602 156 : decoded_salt_buf = palloc(decoded_len);
603 156 : decoded_len = pg_b64_decode(salt_str, strlen(salt_str),
604 : decoded_salt_buf, decoded_len);
605 156 : if (decoded_len < 0)
606 0 : goto invalid_secret;
607 156 : *salt = pstrdup(salt_str);
608 :
609 : /*
610 : * Decode StoredKey and ServerKey.
611 : */
612 156 : decoded_len = pg_b64_dec_len(strlen(storedkey_str));
613 156 : decoded_stored_buf = palloc(decoded_len);
614 156 : decoded_len = pg_b64_decode(storedkey_str, strlen(storedkey_str),
615 : decoded_stored_buf, decoded_len);
616 156 : if (decoded_len != SCRAM_KEY_LEN)
617 8 : goto invalid_secret;
618 148 : memcpy(stored_key, decoded_stored_buf, SCRAM_KEY_LEN);
619 :
620 148 : decoded_len = pg_b64_dec_len(strlen(serverkey_str));
621 148 : decoded_server_buf = palloc(decoded_len);
622 148 : decoded_len = pg_b64_decode(serverkey_str, strlen(serverkey_str),
623 : decoded_server_buf, decoded_len);
624 148 : if (decoded_len != SCRAM_KEY_LEN)
625 8 : goto invalid_secret;
626 140 : memcpy(server_key, decoded_server_buf, SCRAM_KEY_LEN);
627 :
628 140 : return true;
629 :
630 152 : invalid_secret:
631 152 : *salt = NULL;
632 152 : return false;
633 : }
634 :
635 : /*
636 : * Generate plausible SCRAM secret parameters for mock authentication.
637 : *
638 : * In a normal authentication, these are extracted from the secret
639 : * stored in the server. This function generates values that look
640 : * realistic, for when there is no stored secret.
641 : *
642 : * Like in parse_scram_secret(), for 'stored_key' and 'server_key', the
643 : * caller must pass pre-allocated buffers of size SCRAM_KEY_LEN, and
644 : * the buffer for the salt is palloc'd by this function.
645 : */
646 : static void
647 2 : mock_scram_secret(const char *username, int *iterations, char **salt,
648 : uint8 *stored_key, uint8 *server_key)
649 : {
650 : char *raw_salt;
651 : char *encoded_salt;
652 : int encoded_len;
653 :
654 : /* Generate deterministic salt */
655 2 : raw_salt = scram_mock_salt(username);
656 :
657 2 : encoded_len = pg_b64_enc_len(SCRAM_DEFAULT_SALT_LEN);
658 : /* don't forget the zero-terminator */
659 2 : encoded_salt = (char *) palloc(encoded_len + 1);
660 2 : encoded_len = pg_b64_encode(raw_salt, SCRAM_DEFAULT_SALT_LEN, encoded_salt,
661 : encoded_len);
662 :
663 : /*
664 : * Note that we cannot reveal any information to an attacker here so the
665 : * error message needs to remain generic. This should never fail anyway
666 : * as the salt generated for mock authentication uses the cluster's nonce
667 : * value.
668 : */
669 2 : if (encoded_len < 0)
670 0 : elog(ERROR, "could not encode salt");
671 2 : encoded_salt[encoded_len] = '\0';
672 :
673 2 : *salt = encoded_salt;
674 2 : *iterations = SCRAM_DEFAULT_ITERATIONS;
675 :
676 : /* StoredKey and ServerKey are not used in a doomed authentication */
677 2 : memset(stored_key, 0, SCRAM_KEY_LEN);
678 2 : memset(server_key, 0, SCRAM_KEY_LEN);
679 2 : }
680 :
681 : /*
682 : * Read the value in a given SCRAM exchange message for given attribute.
683 : */
684 : static char *
685 148 : read_attr_value(char **input, char attr)
686 : {
687 148 : char *begin = *input;
688 : char *end;
689 :
690 148 : if (*begin != attr)
691 0 : ereport(ERROR,
692 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
693 : errmsg("malformed SCRAM message"),
694 : errdetail("Expected attribute \"%c\" but found \"%s\".",
695 : attr, sanitize_char(*begin))));
696 148 : begin++;
697 :
698 148 : if (*begin != '=')
699 0 : ereport(ERROR,
700 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
701 : errmsg("malformed SCRAM message"),
702 : errdetail("Expected character \"=\" for attribute \"%c\".", attr)));
703 148 : begin++;
704 :
705 148 : end = begin;
706 3252 : while (*end && *end != ',')
707 3104 : end++;
708 :
709 148 : if (*end)
710 : {
711 112 : *end = '\0';
712 112 : *input = end + 1;
713 : }
714 : else
715 36 : *input = end;
716 :
717 148 : return begin;
718 : }
719 :
720 : static bool
721 36 : is_scram_printable(char *p)
722 : {
723 : /*------
724 : * Printable characters, as defined by SCRAM spec: (RFC 5802)
725 : *
726 : * printable = %x21-2B / %x2D-7E
727 : * ;; Printable ASCII except ",".
728 : * ;; Note that any "printable" is also
729 : * ;; a valid "value".
730 : *------
731 : */
732 900 : for (; *p; p++)
733 : {
734 864 : if (*p < 0x21 || *p > 0x7E || *p == 0x2C /* comma */ )
735 0 : return false;
736 : }
737 36 : return true;
738 : }
739 :
740 : /*
741 : * Convert an arbitrary byte to printable form. For error messages.
742 : *
743 : * If it's a printable ASCII character, print it as a single character.
744 : * otherwise, print it in hex.
745 : *
746 : * The returned pointer points to a static buffer.
747 : */
748 : static char *
749 0 : sanitize_char(char c)
750 : {
751 : static char buf[5];
752 :
753 0 : if (c >= 0x21 && c <= 0x7E)
754 0 : snprintf(buf, sizeof(buf), "'%c'", c);
755 : else
756 0 : snprintf(buf, sizeof(buf), "0x%02x", (unsigned char) c);
757 0 : return buf;
758 : }
759 :
760 : /*
761 : * Convert an arbitrary string to printable form, for error messages.
762 : *
763 : * Anything that's not a printable ASCII character is replaced with
764 : * '?', and the string is truncated at 30 characters.
765 : *
766 : * The returned pointer points to a static buffer.
767 : */
768 : static char *
769 0 : sanitize_str(const char *s)
770 : {
771 : static char buf[30 + 1];
772 : int i;
773 :
774 0 : for (i = 0; i < sizeof(buf) - 1; i++)
775 : {
776 0 : char c = s[i];
777 :
778 0 : if (c == '\0')
779 0 : break;
780 :
781 0 : if (c >= 0x21 && c <= 0x7E)
782 0 : buf[i] = c;
783 : else
784 0 : buf[i] = '?';
785 : }
786 0 : buf[i] = '\0';
787 0 : return buf;
788 : }
789 :
790 : /*
791 : * Read the next attribute and value in a SCRAM exchange message.
792 : *
793 : * The attribute character is set in *attr_p, the attribute value is the
794 : * return value.
795 : */
796 : static char *
797 36 : read_any_attr(char **input, char *attr_p)
798 : {
799 36 : char *begin = *input;
800 : char *end;
801 36 : char attr = *begin;
802 :
803 36 : if (attr == '\0')
804 0 : ereport(ERROR,
805 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
806 : errmsg("malformed SCRAM message"),
807 : errdetail("Attribute expected, but found end of string.")));
808 :
809 : /*------
810 : * attr-val = ALPHA "=" value
811 : * ;; Generic syntax of any attribute sent
812 : * ;; by server or client
813 : *------
814 : */
815 36 : if (!((attr >= 'A' && attr <= 'Z') ||
816 36 : (attr >= 'a' && attr <= 'z')))
817 0 : ereport(ERROR,
818 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
819 : errmsg("malformed SCRAM message"),
820 : errdetail("Attribute expected, but found invalid character \"%s\".",
821 : sanitize_char(attr))));
822 36 : if (attr_p)
823 36 : *attr_p = attr;
824 36 : begin++;
825 :
826 36 : if (*begin != '=')
827 0 : ereport(ERROR,
828 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
829 : errmsg("malformed SCRAM message"),
830 : errdetail("Expected character \"=\" for attribute \"%c\".", attr)));
831 36 : begin++;
832 :
833 36 : end = begin;
834 1620 : while (*end && *end != ',')
835 1584 : end++;
836 :
837 36 : if (*end)
838 : {
839 0 : *end = '\0';
840 0 : *input = end + 1;
841 : }
842 : else
843 36 : *input = end;
844 :
845 36 : return begin;
846 : }
847 :
848 : /*
849 : * Read and parse the first message from client in the context of a SCRAM
850 : * authentication exchange message.
851 : *
852 : * At this stage, any errors will be reported directly with ereport(ERROR).
853 : */
854 : static void
855 36 : read_client_first_message(scram_state *state, const char *input)
856 : {
857 36 : char *p = pstrdup(input);
858 : char *channel_binding_type;
859 :
860 :
861 : /*------
862 : * The syntax for the client-first-message is: (RFC 5802)
863 : *
864 : * saslname = 1*(value-safe-char / "=2C" / "=3D")
865 : * ;; Conforms to <value>.
866 : *
867 : * authzid = "a=" saslname
868 : * ;; Protocol specific.
869 : *
870 : * cb-name = 1*(ALPHA / DIGIT / "." / "-")
871 : * ;; See RFC 5056, Section 7.
872 : * ;; E.g., "tls-server-end-point" or
873 : * ;; "tls-unique".
874 : *
875 : * gs2-cbind-flag = ("p=" cb-name) / "n" / "y"
876 : * ;; "n" -> client doesn't support channel binding.
877 : * ;; "y" -> client does support channel binding
878 : * ;; but thinks the server does not.
879 : * ;; "p" -> client requires channel binding.
880 : * ;; The selected channel binding follows "p=".
881 : *
882 : * gs2-header = gs2-cbind-flag "," [ authzid ] ","
883 : * ;; GS2 header for SCRAM
884 : * ;; (the actual GS2 header includes an optional
885 : * ;; flag to indicate that the GSS mechanism is not
886 : * ;; "standard", but since SCRAM is "standard", we
887 : * ;; don't include that flag).
888 : *
889 : * username = "n=" saslname
890 : * ;; Usernames are prepared using SASLprep.
891 : *
892 : * reserved-mext = "m=" 1*(value-char)
893 : * ;; Reserved for signaling mandatory extensions.
894 : * ;; The exact syntax will be defined in
895 : * ;; the future.
896 : *
897 : * nonce = "r=" c-nonce [s-nonce]
898 : * ;; Second part provided by server.
899 : *
900 : * c-nonce = printable
901 : *
902 : * client-first-message-bare =
903 : * [reserved-mext ","]
904 : * username "," nonce ["," extensions]
905 : *
906 : * client-first-message =
907 : * gs2-header client-first-message-bare
908 : *
909 : * For example:
910 : * n,,n=user,r=fyko+d2lbbFgONRv9qkxdawL
911 : *
912 : * The "n,," in the beginning means that the client doesn't support
913 : * channel binding, and no authzid is given. "n=user" is the username.
914 : * However, in PostgreSQL the username is sent in the startup packet, and
915 : * the username in the SCRAM exchange is ignored. libpq always sends it
916 : * as an empty string. The last part, "r=fyko+d2lbbFgONRv9qkxdawL" is
917 : * the client nonce.
918 : *------
919 : */
920 :
921 : /*
922 : * Read gs2-cbind-flag. (For details see also RFC 5802 Section 6 "Channel
923 : * Binding".)
924 : */
925 36 : state->cbind_flag = *p;
926 36 : switch (*p)
927 : {
928 32 : case 'n':
929 :
930 : /*
931 : * The client does not support channel binding or has simply
932 : * decided to not use it. In that case just let it go.
933 : */
934 32 : if (state->channel_binding_in_use)
935 0 : ereport(ERROR,
936 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
937 : errmsg("malformed SCRAM message"),
938 : errdetail("The client selected SCRAM-SHA-256-PLUS, but the SCRAM message does not include channel binding data.")));
939 :
940 32 : p++;
941 32 : if (*p != ',')
942 0 : ereport(ERROR,
943 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
944 : errmsg("malformed SCRAM message"),
945 : errdetail("Comma expected, but found character \"%s\".",
946 : sanitize_char(*p))));
947 32 : p++;
948 32 : break;
949 0 : case 'y':
950 :
951 : /*
952 : * The client supports channel binding and thinks that the server
953 : * does not. In this case, the server must fail authentication if
954 : * it supports channel binding.
955 : */
956 0 : if (state->channel_binding_in_use)
957 0 : ereport(ERROR,
958 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
959 : errmsg("malformed SCRAM message"),
960 : errdetail("The client selected SCRAM-SHA-256-PLUS, but the SCRAM message does not include channel binding data.")));
961 :
962 : #ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
963 0 : if (state->port->ssl_in_use)
964 0 : ereport(ERROR,
965 : (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
966 : errmsg("SCRAM channel binding negotiation error"),
967 : errdetail("The client supports SCRAM channel binding but thinks the server does not. "
968 : "However, this server does support channel binding.")));
969 : #endif
970 0 : p++;
971 0 : if (*p != ',')
972 0 : ereport(ERROR,
973 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
974 : errmsg("malformed SCRAM message"),
975 : errdetail("Comma expected, but found character \"%s\".",
976 : sanitize_char(*p))));
977 0 : p++;
978 0 : break;
979 4 : case 'p':
980 :
981 : /*
982 : * The client requires channel binding. Channel binding type
983 : * follows, e.g., "p=tls-server-end-point".
984 : */
985 4 : if (!state->channel_binding_in_use)
986 0 : ereport(ERROR,
987 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
988 : errmsg("malformed SCRAM message"),
989 : errdetail("The client selected SCRAM-SHA-256 without channel binding, but the SCRAM message includes channel binding data.")));
990 :
991 4 : channel_binding_type = read_attr_value(&p, 'p');
992 :
993 : /*
994 : * The only channel binding type we support is
995 : * tls-server-end-point.
996 : */
997 4 : if (strcmp(channel_binding_type, "tls-server-end-point") != 0)
998 0 : ereport(ERROR,
999 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1000 : errmsg("unsupported SCRAM channel-binding type \"%s\"",
1001 : sanitize_str(channel_binding_type))));
1002 4 : break;
1003 0 : default:
1004 0 : ereport(ERROR,
1005 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1006 : errmsg("malformed SCRAM message"),
1007 : errdetail("Unexpected channel-binding flag \"%s\".",
1008 : sanitize_char(*p))));
1009 : }
1010 :
1011 : /*
1012 : * Forbid optional authzid (authorization identity). We don't support it.
1013 : */
1014 36 : if (*p == 'a')
1015 0 : ereport(ERROR,
1016 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1017 : errmsg("client uses authorization identity, but it is not supported")));
1018 36 : if (*p != ',')
1019 0 : ereport(ERROR,
1020 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1021 : errmsg("malformed SCRAM message"),
1022 : errdetail("Unexpected attribute \"%s\" in client-first-message.",
1023 : sanitize_char(*p))));
1024 36 : p++;
1025 :
1026 36 : state->client_first_message_bare = pstrdup(p);
1027 :
1028 : /*
1029 : * Any mandatory extensions would go here. We don't support any.
1030 : *
1031 : * RFC 5802 specifies error code "e=extensions-not-supported" for this,
1032 : * but it can only be sent in the server-final message. We prefer to fail
1033 : * immediately (which the RFC also allows).
1034 : */
1035 36 : if (*p == 'm')
1036 0 : ereport(ERROR,
1037 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1038 : errmsg("client requires an unsupported SCRAM extension")));
1039 :
1040 : /*
1041 : * Read username. Note: this is ignored. We use the username from the
1042 : * startup message instead, still it is kept around if provided as it
1043 : * proves to be useful for debugging purposes.
1044 : */
1045 36 : state->client_username = read_attr_value(&p, 'n');
1046 :
1047 : /* read nonce and check that it is made of only printable characters */
1048 36 : state->client_nonce = read_attr_value(&p, 'r');
1049 36 : if (!is_scram_printable(state->client_nonce))
1050 0 : ereport(ERROR,
1051 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1052 : errmsg("non-printable characters in SCRAM nonce")));
1053 :
1054 : /*
1055 : * There can be any number of optional extensions after this. We don't
1056 : * support any extensions, so ignore them.
1057 : */
1058 36 : while (*p != '\0')
1059 0 : read_any_attr(&p, NULL);
1060 :
1061 : /* success! */
1062 36 : }
1063 :
1064 : /*
1065 : * Verify the final nonce contained in the last message received from
1066 : * client in an exchange.
1067 : */
1068 : static bool
1069 36 : verify_final_nonce(scram_state *state)
1070 : {
1071 36 : int client_nonce_len = strlen(state->client_nonce);
1072 36 : int server_nonce_len = strlen(state->server_nonce);
1073 36 : int final_nonce_len = strlen(state->client_final_nonce);
1074 :
1075 36 : if (final_nonce_len != client_nonce_len + server_nonce_len)
1076 0 : return false;
1077 36 : if (memcmp(state->client_final_nonce, state->client_nonce, client_nonce_len) != 0)
1078 0 : return false;
1079 36 : if (memcmp(state->client_final_nonce + client_nonce_len, state->server_nonce, server_nonce_len) != 0)
1080 0 : return false;
1081 :
1082 36 : return true;
1083 : }
1084 :
1085 : /*
1086 : * Verify the client proof contained in the last message received from
1087 : * client in an exchange.
1088 : */
1089 : static bool
1090 36 : verify_client_proof(scram_state *state)
1091 : {
1092 : uint8 ClientSignature[SCRAM_KEY_LEN];
1093 : uint8 ClientKey[SCRAM_KEY_LEN];
1094 : uint8 client_StoredKey[SCRAM_KEY_LEN];
1095 : scram_HMAC_ctx ctx;
1096 : int i;
1097 :
1098 : /* calculate ClientSignature */
1099 36 : scram_HMAC_init(&ctx, state->StoredKey, SCRAM_KEY_LEN);
1100 72 : scram_HMAC_update(&ctx,
1101 36 : state->client_first_message_bare,
1102 36 : strlen(state->client_first_message_bare));
1103 36 : scram_HMAC_update(&ctx, ",", 1);
1104 72 : scram_HMAC_update(&ctx,
1105 36 : state->server_first_message,
1106 36 : strlen(state->server_first_message));
1107 36 : scram_HMAC_update(&ctx, ",", 1);
1108 72 : scram_HMAC_update(&ctx,
1109 36 : state->client_final_message_without_proof,
1110 36 : strlen(state->client_final_message_without_proof));
1111 36 : scram_HMAC_final(ClientSignature, &ctx);
1112 :
1113 : /* Extract the ClientKey that the client calculated from the proof */
1114 1188 : for (i = 0; i < SCRAM_KEY_LEN; i++)
1115 1152 : ClientKey[i] = state->ClientProof[i] ^ ClientSignature[i];
1116 :
1117 : /* Hash it one more time, and compare with StoredKey */
1118 36 : scram_H(ClientKey, SCRAM_KEY_LEN, client_StoredKey);
1119 :
1120 36 : if (memcmp(client_StoredKey, state->StoredKey, SCRAM_KEY_LEN) != 0)
1121 10 : return false;
1122 :
1123 26 : return true;
1124 : }
1125 :
1126 : /*
1127 : * Build the first server-side message sent to the client in a SCRAM
1128 : * communication exchange.
1129 : */
1130 : static char *
1131 36 : build_server_first_message(scram_state *state)
1132 : {
1133 : /*------
1134 : * The syntax for the server-first-message is: (RFC 5802)
1135 : *
1136 : * server-first-message =
1137 : * [reserved-mext ","] nonce "," salt ","
1138 : * iteration-count ["," extensions]
1139 : *
1140 : * nonce = "r=" c-nonce [s-nonce]
1141 : * ;; Second part provided by server.
1142 : *
1143 : * c-nonce = printable
1144 : *
1145 : * s-nonce = printable
1146 : *
1147 : * salt = "s=" base64
1148 : *
1149 : * iteration-count = "i=" posit-number
1150 : * ;; A positive number.
1151 : *
1152 : * Example:
1153 : *
1154 : * r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,s=QSXCR+Q6sek8bf92,i=4096
1155 : *------
1156 : */
1157 :
1158 : /*
1159 : * Per the spec, the nonce may consist of any printable ASCII characters.
1160 : * For convenience, however, we don't use the whole range available,
1161 : * rather, we generate some random bytes, and base64 encode them.
1162 : */
1163 : char raw_nonce[SCRAM_RAW_NONCE_LEN];
1164 : int encoded_len;
1165 :
1166 36 : if (!pg_strong_random(raw_nonce, SCRAM_RAW_NONCE_LEN))
1167 0 : ereport(ERROR,
1168 : (errcode(ERRCODE_INTERNAL_ERROR),
1169 : errmsg("could not generate random nonce")));
1170 :
1171 36 : encoded_len = pg_b64_enc_len(SCRAM_RAW_NONCE_LEN);
1172 : /* don't forget the zero-terminator */
1173 36 : state->server_nonce = palloc(encoded_len + 1);
1174 36 : encoded_len = pg_b64_encode(raw_nonce, SCRAM_RAW_NONCE_LEN,
1175 : state->server_nonce, encoded_len);
1176 36 : if (encoded_len < 0)
1177 0 : ereport(ERROR,
1178 : (errcode(ERRCODE_INTERNAL_ERROR),
1179 : errmsg("could not encode random nonce")));
1180 36 : state->server_nonce[encoded_len] = '\0';
1181 :
1182 36 : state->server_first_message =
1183 36 : psprintf("r=%s%s,s=%s,i=%u",
1184 : state->client_nonce, state->server_nonce,
1185 : state->salt, state->iterations);
1186 :
1187 36 : return pstrdup(state->server_first_message);
1188 : }
1189 :
1190 :
1191 : /*
1192 : * Read and parse the final message received from client.
1193 : */
1194 : static void
1195 36 : read_client_final_message(scram_state *state, const char *input)
1196 : {
1197 : char attr;
1198 : char *channel_binding;
1199 : char *value;
1200 : char *begin,
1201 : *proof;
1202 : char *p;
1203 : char *client_proof;
1204 : int client_proof_len;
1205 :
1206 36 : begin = p = pstrdup(input);
1207 :
1208 : /*------
1209 : * The syntax for the server-first-message is: (RFC 5802)
1210 : *
1211 : * gs2-header = gs2-cbind-flag "," [ authzid ] ","
1212 : * ;; GS2 header for SCRAM
1213 : * ;; (the actual GS2 header includes an optional
1214 : * ;; flag to indicate that the GSS mechanism is not
1215 : * ;; "standard", but since SCRAM is "standard", we
1216 : * ;; don't include that flag).
1217 : *
1218 : * cbind-input = gs2-header [ cbind-data ]
1219 : * ;; cbind-data MUST be present for
1220 : * ;; gs2-cbind-flag of "p" and MUST be absent
1221 : * ;; for "y" or "n".
1222 : *
1223 : * channel-binding = "c=" base64
1224 : * ;; base64 encoding of cbind-input.
1225 : *
1226 : * proof = "p=" base64
1227 : *
1228 : * client-final-message-without-proof =
1229 : * channel-binding "," nonce [","
1230 : * extensions]
1231 : *
1232 : * client-final-message =
1233 : * client-final-message-without-proof "," proof
1234 : *------
1235 : */
1236 :
1237 : /*
1238 : * Read channel binding. This repeats the channel-binding flags and is
1239 : * then followed by the actual binding data depending on the type.
1240 : */
1241 36 : channel_binding = read_attr_value(&p, 'c');
1242 36 : if (state->channel_binding_in_use)
1243 : {
1244 : #ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
1245 4 : const char *cbind_data = NULL;
1246 4 : size_t cbind_data_len = 0;
1247 : size_t cbind_header_len;
1248 : char *cbind_input;
1249 : size_t cbind_input_len;
1250 : char *b64_message;
1251 : int b64_message_len;
1252 :
1253 : Assert(state->cbind_flag == 'p');
1254 :
1255 : /* Fetch hash data of server's SSL certificate */
1256 4 : cbind_data = be_tls_get_certificate_hash(state->port,
1257 : &cbind_data_len);
1258 :
1259 : /* should not happen */
1260 4 : if (cbind_data == NULL || cbind_data_len == 0)
1261 0 : elog(ERROR, "could not get server certificate hash");
1262 :
1263 4 : cbind_header_len = strlen("p=tls-server-end-point,,"); /* p=type,, */
1264 4 : cbind_input_len = cbind_header_len + cbind_data_len;
1265 4 : cbind_input = palloc(cbind_input_len);
1266 4 : snprintf(cbind_input, cbind_input_len, "p=tls-server-end-point,,");
1267 4 : memcpy(cbind_input + cbind_header_len, cbind_data, cbind_data_len);
1268 :
1269 4 : b64_message_len = pg_b64_enc_len(cbind_input_len);
1270 : /* don't forget the zero-terminator */
1271 4 : b64_message = palloc(b64_message_len + 1);
1272 4 : b64_message_len = pg_b64_encode(cbind_input, cbind_input_len,
1273 : b64_message, b64_message_len);
1274 4 : if (b64_message_len < 0)
1275 0 : elog(ERROR, "could not encode channel binding data");
1276 4 : b64_message[b64_message_len] = '\0';
1277 :
1278 : /*
1279 : * Compare the value sent by the client with the value expected by the
1280 : * server.
1281 : */
1282 4 : if (strcmp(channel_binding, b64_message) != 0)
1283 0 : ereport(ERROR,
1284 : (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
1285 : errmsg("SCRAM channel binding check failed")));
1286 : #else
1287 : /* shouldn't happen, because we checked this earlier already */
1288 : elog(ERROR, "channel binding not supported by this build");
1289 : #endif
1290 : }
1291 : else
1292 : {
1293 : /*
1294 : * If we are not using channel binding, the binding data is expected
1295 : * to always be "biws", which is "n,," base64-encoded, or "eSws",
1296 : * which is "y,,". We also have to check whether the flag is the same
1297 : * one that the client originally sent.
1298 : */
1299 32 : if (!(strcmp(channel_binding, "biws") == 0 && state->cbind_flag == 'n') &&
1300 0 : !(strcmp(channel_binding, "eSws") == 0 && state->cbind_flag == 'y'))
1301 0 : ereport(ERROR,
1302 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1303 : errmsg("unexpected SCRAM channel-binding attribute in client-final-message")));
1304 : }
1305 :
1306 36 : state->client_final_nonce = read_attr_value(&p, 'r');
1307 :
1308 : /* ignore optional extensions, read until we find "p" attribute */
1309 : do
1310 : {
1311 36 : proof = p - 1;
1312 36 : value = read_any_attr(&p, &attr);
1313 36 : } while (attr != 'p');
1314 :
1315 36 : client_proof_len = pg_b64_dec_len(strlen(value));
1316 36 : client_proof = palloc(client_proof_len);
1317 36 : if (pg_b64_decode(value, strlen(value), client_proof,
1318 : client_proof_len) != SCRAM_KEY_LEN)
1319 0 : ereport(ERROR,
1320 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1321 : errmsg("malformed SCRAM message"),
1322 : errdetail("Malformed proof in client-final-message.")));
1323 36 : memcpy(state->ClientProof, client_proof, SCRAM_KEY_LEN);
1324 36 : pfree(client_proof);
1325 :
1326 36 : if (*p != '\0')
1327 0 : ereport(ERROR,
1328 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1329 : errmsg("malformed SCRAM message"),
1330 : errdetail("Garbage found at the end of client-final-message.")));
1331 :
1332 36 : state->client_final_message_without_proof = palloc(proof - begin + 1);
1333 36 : memcpy(state->client_final_message_without_proof, input, proof - begin);
1334 36 : state->client_final_message_without_proof[proof - begin] = '\0';
1335 36 : }
1336 :
1337 : /*
1338 : * Build the final server-side message of an exchange.
1339 : */
1340 : static char *
1341 26 : build_server_final_message(scram_state *state)
1342 : {
1343 : uint8 ServerSignature[SCRAM_KEY_LEN];
1344 : char *server_signature_base64;
1345 : int siglen;
1346 : scram_HMAC_ctx ctx;
1347 :
1348 : /* calculate ServerSignature */
1349 26 : scram_HMAC_init(&ctx, state->ServerKey, SCRAM_KEY_LEN);
1350 52 : scram_HMAC_update(&ctx,
1351 26 : state->client_first_message_bare,
1352 26 : strlen(state->client_first_message_bare));
1353 26 : scram_HMAC_update(&ctx, ",", 1);
1354 52 : scram_HMAC_update(&ctx,
1355 26 : state->server_first_message,
1356 26 : strlen(state->server_first_message));
1357 26 : scram_HMAC_update(&ctx, ",", 1);
1358 52 : scram_HMAC_update(&ctx,
1359 26 : state->client_final_message_without_proof,
1360 26 : strlen(state->client_final_message_without_proof));
1361 26 : scram_HMAC_final(ServerSignature, &ctx);
1362 :
1363 26 : siglen = pg_b64_enc_len(SCRAM_KEY_LEN);
1364 : /* don't forget the zero-terminator */
1365 26 : server_signature_base64 = palloc(siglen + 1);
1366 26 : siglen = pg_b64_encode((const char *) ServerSignature,
1367 : SCRAM_KEY_LEN, server_signature_base64,
1368 : siglen);
1369 26 : if (siglen < 0)
1370 0 : elog(ERROR, "could not encode server signature");
1371 26 : server_signature_base64[siglen] = '\0';
1372 :
1373 : /*------
1374 : * The syntax for the server-final-message is: (RFC 5802)
1375 : *
1376 : * verifier = "v=" base64
1377 : * ;; base-64 encoded ServerSignature.
1378 : *
1379 : * server-final-message = (server-error / verifier)
1380 : * ["," extensions]
1381 : *
1382 : *------
1383 : */
1384 26 : return psprintf("v=%s", server_signature_base64);
1385 : }
1386 :
1387 :
1388 : /*
1389 : * Deterministically generate salt for mock authentication, using a SHA256
1390 : * hash based on the username and a cluster-level secret key. Returns a
1391 : * pointer to a static buffer of size SCRAM_DEFAULT_SALT_LEN.
1392 : */
1393 : static char *
1394 2 : scram_mock_salt(const char *username)
1395 : {
1396 : pg_sha256_ctx ctx;
1397 : static uint8 sha_digest[PG_SHA256_DIGEST_LENGTH];
1398 2 : char *mock_auth_nonce = GetMockAuthenticationNonce();
1399 :
1400 : /*
1401 : * Generate salt using a SHA256 hash of the username and the cluster's
1402 : * mock authentication nonce. (This works as long as the salt length is
1403 : * not larger the SHA256 digest length. If the salt is smaller, the caller
1404 : * will just ignore the extra data.)
1405 : */
1406 : StaticAssertStmt(PG_SHA256_DIGEST_LENGTH >= SCRAM_DEFAULT_SALT_LEN,
1407 : "salt length greater than SHA256 digest length");
1408 :
1409 2 : pg_sha256_init(&ctx);
1410 2 : pg_sha256_update(&ctx, (uint8 *) username, strlen(username));
1411 2 : pg_sha256_update(&ctx, (uint8 *) mock_auth_nonce, MOCK_AUTH_NONCE_LEN);
1412 2 : pg_sha256_final(&ctx, sha_digest);
1413 :
1414 2 : return (char *) sha_digest;
1415 : }
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